<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <button class="btn">点击</button>
</body>
<script>
  const btn = document.querySelector('.btn');
  console.log(btn)
  btn.addEventListener('click', function () {
    console.log('按钮被点击了')
  })
</script>

</html>